Juniper JUNOSE 11.2.X IP SERVICES, Configuration Manual

Page: 64 / 356

A community list is a sequential collection of permit and deny conditions. Each condition
describes the community number to be matched. If you issued the
ip bgp-community
new-format command, the community number is in AA : NN format; otherwise, it is in
decimal format (the hexadecimal octets converted to decimal).
The router tests the community attribute of a route against each condition in a community
list. The first match determines whether the router accepts (the route is permitted) or
rejects (the route is denied) a route that has the specified community. Because the router
stops testing conditions after the first match, the order of the conditions is critical. If no
conditions match, the router rejects the route.
Consider the network structure shown in Figure 5 on page 38.
Figure 5: Community Lists
Suppose you want router Albany to set metrics for routes that it forwards to router Boston
based on the communities to which the routes belong. You can create community lists
and filter the routes with a route map that matches on the community list. The following
example configures router Albany:
host1(config)# router bgp 293
host1(config-router)# neighbor 10.5.5.2 remote-as 32
host1(config-router)# neighbor 10.2.2.1 remote-as 451
host1(config-router)# neighbor 10.2.2.4 remote-as 17
host1(config-router)# neighbor 10.2.2.4 route-map commtrc out
host1(config-router)# exit
host1(config)# route-map commtrc permit 1
host1(config-route-map)# match community 1
host1(config-route-map)# set metric 20
host1(config-route-map)# exit
host1(config)# route-map commtrc permit 2
host1(config-route-map)# match community 2
host1(config-route-map)# set metric 75
host1(config-route-map)# exit
host1(config)# route-map commtrc permit 3
host1(config-route-map)# match community 3
host1(config-route-map)# set metric 85
Copyright © 2010, Juniper Networks, Inc. 38
JunosE 11.2.x IP Services Configuration Guide